Systems and methods for visualizing interior tissue regions using expandable imaging structures

ABSTRACT

An imaging structure has a periphery adapted to selectively assume an expanded geometry and a collapsed geometry. The periphery of the imaging structure carries an array of spaced apart ultrasound transducers.

FIELD OF THE INVENTION

In a general sense, the invention is directed to systems and methods forvisualizing interior regions of the human body. In a more particularsense, the invention is directed to systems and methods for mapping orablating heart tissue for treating cardiac conditions.

BACKGROUND OF THE INVENTION

Systems and methods for visualizing interior regions of a living bodyare known. For example, ultrasound systems and methods are shown anddescribed in Yock U.S. Pat. Nos. 5,313,949 and Webler et al. 5,485,846.

Due to dynamic forces within the body, it can be difficult to stabilizeinternal imaging devices to consistently generate accurate images havingthe quality required to prescribe appropriate treatment or therapy.There is often an attendant need to constantly position and repositionthe image acquisition element. In addition, tissue and anatomicstructures inside the body can contact and occlude the image acquisitionelement.

External imaging modalities are available. Still, these alternativemodalities have their own shortcomings.

For example, in carrying out endocardial ablation procedures,fluoroscopic imaging is widely used to identify anatomic landmarkswithin the heart. Fluoroscopic imaging is also widely used to locate theposition of the ablation electrode or electrodes relative to thetargeted ablation site. It is often difficult to identify these anatomicsites using fluoroscopy. It is also difficult, if not impossible, to usefluoroscopy to ascertain that the desired lesion pattern has beencreated after ablation. Often, the achievement of desired lesioncharacteristics must be inferred based upon measurements of appliedablation power, system impedance, tissue temperature, and ablation time.Furthermore, fluoroscopy cannot readily locate the border zones betweeninfarcted tissue and normal tissue, where efficacious ablation zones arebelieved to reside.

SUMMARY OF THE INVENTION

The invention provides improved systems and methods to visualizeinterior body regions. The systems and methods provide an imagingstructure having a periphery adapted to selectively assume an expandedgeometry and a collapsed geometry. The periphery of the imagingstructure carries an array of spaced apart ultrasound transducers.

In a preferred embodiment, the system and methods guide the imagingstructure into the interior body region, with the imaging structureassuming the collapsed geometry. The systems and methods cause theimaging structure to assume the expanded geometry upon arrival in theinterior body region. In this expanded geometry, the systems and methodsoperate the imaging structure to visualize tissue in the interior bodyregion.

In a preferred embodiment, the systems and methods move the imagingstructure within a support structure, which extends beyond the peripheryof the imaging structure. The support structure stabilizes the imagingstructure, while the imaging structure visualizes tissue in the interiorbody region. The support structure resists dislodgment or disorientationof the imaging structure, despite the presence of dynamic forces.

In a preferred embodiment, the array comprises a phased array ofultrasound transducers.

Other features and advantages of the inventions are set forth in thefollowing Description and Drawings, as well as in the appended Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a system for visualizing tissue that includes asupport structure carrying an imaging probe;

FIG. 2 is a side section view of the imaging probe and support structureof FIG. 1 in a collapsed condition within an external slidable sheath;

FIG. 3 is a side section view of a portion of a spline that forms a partof the support structure shown in FIG. 1;

FIGS. 4A and 4B are side sectional, somewhat diagrammatic views of thedeployment of the support structure and imaging probe shown in FIG. 1within a heart chamber;

FIG. 5A is a side section view of the support structure and imagingprobe shown in FIG. 1, showing various paths in which the imaging probecan be moved when located within a body region;

FIG. 5B is a side view of an alternative embodiment of an imaging probeand a support structure comprising a single spline element;

FIG. 6 is an enlarged view of one embodiment of the support structureand imaging probe, in which the imaging probe includes a rotatingultrasonic transducer crystal;

FIG. 7 is an enlarged view of another embodiment of the supportstructure and imaging probe, in which the imaging probe includes a fiberoptic assembly;

FIG. 8 is a partial side section, perspective, and largely schematic,view of a support structure and imaging probe as shown in FIG. 1, inwhich the imaging probe is associated with a system to conduct contrastechocardiography to identify potential ablation sites by imaging tissueperfusion;

FIG. 9 is a partial side section, largely schematic view of the supportstructure and imaging probe shown in FIG. 1, including anelectro-mechanical axial translator connected to the imaging probe;

FIG. 10 is a side section view, somewhat diagrammatic is nature, showinga support structure and imaging probe, in which both the structure andthe probe carry electrodes;

FIG. 11 is a side section view of a portion of an electrode-carryingspline that forms a part of the support structure shown in FIG. 10;

FIG. 12 is a side section view of a heart and a perspective view of thesupport structure and imaging probe shown in FIG. 10, being used inassociation with a separate roving mapping, pacing, or ablatingelectrode;

FIG. 13A is a side view, with portions removed, of a support assemblycomprising a expanded porous body capable of ionic transfer of ablationenergy, which carries an interior imaging probe;

FIG. 13B is a side elevation view of the porous body shown in FIG. 13A,with the porous body shown in a collapsed condition for introductioninto an interior body region;

FIG. 14 is a side view of a support assembly carrying within it theporous body and imaging probe assembly shown in FIGS. 13A and 13B;

FIG. 15 is a side view, somewhat diagrammatic in form, showing a supportstructure that carries within it a movable imaging probe, the supportstructure also carrying multiple electrodes sized to create long lesionpatterns;

FIG. 16 is an illustration representative of a typical small tissuelesion pattern;

FIG. 17 is an illustration representative of a typical larger tissuelesion pattern;

FIG. 18 is an illustration representative of a typical long tissuelesion pattern;

FIG. 19 is an illustration representative of a typical complex longtissue lesion pattern;

FIG. 20 is an illustration representative of a typical segmented tissuelesion pattern;

FIG. 21 is a side section view, somewhat diagrammatic in form, showing asupport structure that carries within it an image acquisition elementgated according to intracardiac activation sensed by an electrode alsocarried by the support structure;

FIG. 22 is a side section view, somewhat diagrammatic in form, of asupport structure that carries within it an image acquisition element,also shown with an enlarged perspective view, comprising a phasedtransducer array that includes multiple transducers panels scored ondifferent planar sections of a piezoelectric material;

FIG. 23 is a side section view of a support structure that carrieswithin it an image acquisition element comprising a phased multipletransducer array carried on flexible spline elements;

FIG. 24 is a side section view of a support structure that carrieswithin it an image acquisition element comprising a phased multipletransducer array carried on an expandable-collapsible body;

FIG. 25 is a side section view, somewhat diagrammatic in form, of asupport structure that carries within it an image acquisition elementcomprising an optical coherence domain reflectometer;

FIG. 26 is a diagrammatic view of a system for identifying the physicalcharacteristics of a support structure using a machine-readable code, toenable the creation of a positioning matrix (shown in FIG. 10) to guidethe imaging probe within the structure;

FIG. 27 is a diagrammatic view of one implementation of themachine-readable code used to identify the individual physicalcharacteristics of the support structure shown in FIG. 26; and

FIG. 28 is a diagrammatic view of another implementation of themachine-readable code used to identify the individual physicalcharacteristics of the support structure shown in FIG. 26.

The invention may be embodied in several forms without departing fromits spirit or essential characteristics. The scope of the invention isdefined in the appended claims, rather than in the specific descriptionpreceding them. All embodiments that fall within the meaning and rangeof equivalency of the claims are therefore intended to be embraced bythe claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a system 10, which embodies features of the invention, forvisualizing interior regions of a living body. The invention is welladapted for use inside body lumens, chambers or cavities for eitherdiagnostic or therapeutic purposes. It particularly lends itself tocatheter-based procedures, where access to the interior body region isobtained, for example, through the vascular system or alimentary canal,without complex, invasive surgical procedures.

The invention may be used in diverse body regions for diagnosing ortreating diseases. For example, various aspects of the invention haveapplication for the diagnosis and treatment of arrhythmia conditionswithin the heart, such as ventricular tachycardia or atrialfibrillation. The invention also has application in the diagnosis ortreatment of intravascular ailments, in association, for example, withangioplasty or atherectomy techniques. Various aspects of the inventionalso have application for diagnosis or treatment of ailments in thegastrointestinal tract, the prostrate, brain, gall bladder, uterus, andother regions of the body. The invention can also be used in associationwith systems and methods that are not necessarily catheter-based. Thediverse applicability of the invention in these and other fields of usewill become apparent.

I. Visualization for Diagnostic Purposes

The invention makes it possible for a physician to access and visualizeor image inter-body regions, to thereby locate and identifyabnormalities that may be present. The invention provides a stableplatform through which accurate displays of these images can be createdfor viewing and analysis by the physician. Accurate images enable thephysician to prescribe appropriate treatment or therapy.

As implemented in the embodiment shown in FIG. 1, the invention providesa system 10 comprising a support structure 20 that carries within it animaging or visualizing probe 34. As FIG. 1 shows, the system 10 includesa flexible catheter tube 12 with a proximal end 14 and a distal end 16.The proximal end 14 carries an attached handle 18. The distal end 16carries the support structure 20.

A. The Support Structure

The support structure 20 can be constructed in various ways. In onepreferred embodiment (illustrated in FIG. 1), the structure 20 comprisestwo or more flexible spline elements 22. In FIG. 1, the supportstructure 20 includes eight spline elements 22. Of course, fewer or morespline elements 22 can be present. For example, FIG. 5A shows thesupport structure 20 comprising just two, generally oppositely spacedspline elements 22. As another example, FIG. 5B shows the supportstructure 20 comprising a single spline element 22. In FIG. 5B, thedistal end 23 of the spline element 22 is attached to a stylet 25,carried by the catheter tube 12, which moves the distal end 23 (as shownby arrows 27) along the axis of the catheter tube 12 to adjust thecurvature of the spline element 22.

As FIG. 3 shows, each spline element 22 preferably comprises a flexiblecore body 84 enclosed within a flexible, electrically nonconductivesleeve 32. The sleeve 32 is made of, for example, a polymeric,electrically nonconductive material, like polyethylene or polyurethane.The sleeve 32 is preferable heat shrunk about the core body 84.

The core body 84 is made from resilient, inert wire or plastic. Elasticmemory material such as nickel titanium (commercially available asNITINOL™ material) can be used. Resilient injection molded plastic orstainless steel can also be used. Preferably, the core body 84 is athin, rectilinear strip. The rectilinear cross-section impartsresistance to twisting about the longitudinal axis of the core body 84,thereby providing structural stability and good bio-mechanicalproperties. Other cross-sectional configurations, such as cylindrical,can be used, if desired.

The core bodies 84 of the spline elements 22 extend longitudinallybetween a distal hub 24 and a base 26. The base 26 is carried by thedistal end 16 of the catheter tube 12. As FIG. 1 shows, each core body84 is preformed with a convex bias, creating a normally openthree-dimensional basket structure expanded about a main center axis 89.

As FIG. 2 shows, in the illustrated and preferred embodiment, the system10 includes an outer sheath 44 carried about the catheter tube 12. Thesheath 44 has an inner diameter that is greater than the outer diameterof the catheter tube 12. As a result, the sheath 44 slides along theoutside of the catheter tube 12.

Forward movement (arrow 43) advances the slidable sheath 44 over thesupport structure 20. In this position, the slidable sheath 44compresses and collapses the support structure 20 into a low profile(shown in FIG. 2) for introduction through a vascular or other bodypassage to the intended interior site.

Rearward movement (arrow 45) retracts the slidable sheath 44 away fromthe support structure 20. This removes the compression force. The freedsupport structure 20 opens (as FIG. 1 shows) and assumes itsthree-dimensional shape.

(i) Deployment of the support Assembly

The methodology for deploying the support structure 20 of course variesaccording to the particular inter-body region targeted for access. FIGS.4A and 4B show a representative deployment technique usable whenvascular access to a heart chamber is required.

The physician uses an introducer 85, made from inert plastic materials(e.g., polyester), having a skin-piercing cannula 86. The cannula 86establishes percutaneous access into, for example, the femoral artery88. The exterior end of the introducer 85 includes a conventionalhemostatic valve 90 to block the outflow of blood and other fluids fromthe access. The valve may take the form of a conventional slottedmembrane or conventional shutter valve arrangement (not shown). A valve90 suitable for use may be commercial procured from B. Braun MedicalCompany (Bethlehem, Pa.). The introducer 85 includes a flushing port 87to introduce sterile saline to periodically clean the region of thevalve 90.

As FIG. 4A shows, the physician advances a guide sheath 92 through theintroducer 85 into the accessed artery 88. A guide catheter or guidewire (not shown) may be used in association with the guide sheath 92 toaid in directing the guide sheath 92 through the artery 88 toward theheart 94. It should be noted that the views of the heart 94 and otherinterior regions of the body in this Specification are not intended tobe anatomically accurate in every detail. The Figures show anatomicdetails in diagrammatic form as necessary to show the features of theinvention.

The physician observes the advancement of the guide sheath 92 throughthe artery 88 using fluoroscopic or ultrasound imaging, or the like. Theguide sheath 92 can include a radio-opaque compound, such as barium, forthis purpose. Alternatively, a radio-opaque marker can be placed at thedistal end of the guide sheath 92.

In this way, the physician maneuvers the guide sheath 92 through theartery 88 retrograde past the aortic valve and into the left ventricle98. The guide sheath 92 establishes a passageway through the artery 88into the ventricle 98, without an invasive open heart surgicalprocedure. If an alternative access to the left atrium or ventricle isdesired (as FIG. 15 shows), a conventional transeptal sheath assembly(not shown) can be used to gain passage through the septum between theleft and right atria. Access to the right atrium or ventricle isaccomplished in the same manner, but without advancing the transeptalsheath across the atrial septum.

As FIG. 4A shows, once the guide sheath 92 is placed in the targetedregion, the physician advances the catheter tube 12, with the supportstructure 20 confined within the slidable sheath 44, through the guidesheath 92 and into the targeted region.

As FIG. 4B shows, pulling back upon the slidable sheath 44 (see arrow 45in FIG. 4B) allows the structure 20 to spring open within the targetedregion for use. When deployed for use (as FIG. 4B shows), the shape ofthe support structure 20 (which, in FIG. 4B, is three-dimensional) holdsthe spline elements 22 in intimate contact against the surroundingtissue mass. As will be explained in greater detail later (and as FIG.4B shows), the support structure 20 has an open interior 21, whichsurrounds the imaging probe 34, keeping the tissue mass from contactingit.

As FIGS. 1 and 4B show, the geometry of flexible spline elements 22 isradially symmetric about the main axis 89. That is, the spline elements22 uniformly radiate from the main axis 89 at generally equal arcuate,or circumferential, intervals.

The elements 22 also present a geometry that is axially symmetric alongthe main axis 89. That is, when viewed from the side (as FIGS. 1 and 4Bshow) the proximal and distal regions of the assembled splines 22 haveessentially the same curvilinear geometry along the main axis 89.

Of course, if desired, the spline elements 22 can form various othergeometries that are either radially asymmetric, or axially asymmetric,or both. In this respect, the axial geometry for the structure 20,whether symmetric or asymmetric, is selected to best conform to theexpected interior contour of the body chamber that the structure 20will, in use, occupy. For example, the interior contour of a heartventricle differs from the interior contour of a heart atrium. Theability to provide support structures 20 with differing asymmetricshapes makes it possible to provide one discrete configuration tailoredfor atrial use and another discrete configuration tailored forventricular use. Examples of asymmetric arrays of spline structures 20for use in the heart are shown in copending U.S. application Ser. No.08/728,698 filed Oct. 28, 1996, entitled "Asymmetric Multiple ElectrodeSupport Structures," which is incorporated herein by reference.

B. The Imaging Probe

As FIG. 5A shows, the imaging probe 34 located within the supportstructure 20 includes a flexible body 36, which extends through acentral bore 38 in the catheter tube 12. The body 36 has a distal region40 that projects beyond the distal end 16 of the catheter tube 12 intothe interior of the support structure 20. The body 36 also includes aproximal region 42 that carries an auxiliary handle 46. Anotherconventional hemostatic valve 48 is located at the distal end 16 of thecatheter tube 12 to block the backflow of fluid through the cathetertube 12 while allowing the passage of the body 36.

The distal body region 40 carries an image acquisition element 50, whichwill be called in abbreviated form the IAE. The IAE 50 generatesvisualizing signals representing an image of the area, and objects andtissues that occupy the area, surrounding the structure 20. The IAE 50can be of various constructions.

(i) Ultrasonic Imaging

In one embodiment (see FIG. 6), the IAE 50 comprises an ultrasonictransducer 52. The transducer 52 forms a part of a conventionalultrasound imaging system 54 generally of the type shown in U.S. Pat.No. 5,313,949. This patent is incorporated herein by reference.

The transducer 52 comprises one or more piezoelectric crystals formedof, for example, barium titinate or cinnabar, which is capable ofoperating at a frequency range of 5 to 20 megahertz. Other types ofultrasonic crystal oscillators can be used. For example, organicelectrets such as polyvinylidene difluoride and vinylidenefluoride-trifluoro-ethylene copolymers can also be used.

The imaging system 54 includes a transmitter 56 coupled to thetransducer crystal 52 (see FIG. 6). The transmitter 56 generates voltagepulses (typically in the range of 10 to 150 volts) for excitation of thetransducer crystal 52. The voltage pulses cause the transducer crystal52 to produce sonic waves.

As the transmitter 56 supplies voltage pulses to the transducer crystal52, a motor 58 rotates the transducer crystal 52 (being linked by theflexible drive shaft 53, which passes through a bore in the tube 36).The transmission of voltage pulses (and, thus, the sonic waves) and therotation of the transducer crystal 52 are synchronized by a timing andcontrol element 60. Typically, the motor 58 rotates the transducercrystal 52 in the range of 500 to 2000 rpm, depending upon the framerate of the image desired. The rotating transducer crystal 52 therebyprojects the sonic waves in a 360° pattern into the interior of thechamber or cavity that surrounds it.

Tissue, including tissue forming anatomic structures, such as heartvalves (which is generally designated T in the Figures), and internaltissue structures and deposits or lesions on the tissue, scanned by therotating transducer crystal 52 will scatter the sonic waves. The supportstructure 20 also scatters the sonic waves. The scattered waves returnto the rotating transducer crystal 52. The transducer crystal 52converts the scattered waves into electrical signals. The imaging system54 includes a receiver 57, which amplifies these electrical signals. Theimaging system 54 digitally processes the signals, synchronized by thetiming and control element 60 to the rotation of the transducer crystal52, using known display algorithms; for example, conventional radar(PPI) algorithms. These algorithms are based upon the directrelationship that elapsed time (Δt) between pulse emission and returnecho has to the distance (d) of the tissue from the transducer,expressed as follows:

    d=Δt/2ν

where ν is the speed of sound in the surrounding media.

The digitally processed signals are supplied to a display unit 59. Thedisplay unit 59 comprises a screen, which can be, for example, a CRTmonitor. The display screen 59 shows an ultrasound image or profile inthe desired format, which depicts the tissue and anatomic structuresscanned by the transducer crystal 52. The display screen 59 can providea single or multi-dimensional echocardiograph or a non-imaging A-modedisplay. A control console (not shown) may be provided to allowselection by the physician of the desired display format.

Alternatively, the ultrasonic transducer crystal 52 can be operated inconventional fashion without rotation, as shown in U.S. Pat. Nos.4,697,595, or 4,706,681, or 5,358,148. Each of these patents isincorporated herein by reference.

(ii) Fiber Optic Imaging

In another embodiment (see FIG. 7), the IAE 50 comprises a fiber opticassembly 62, which permits direct visualization of tissue. Various typesof fiber optic assemblies 62 can be used.

The illustrated embodiment employs a fiber optic assembly 62 of the typeshown in U.S. Pat. No. 4,976,710, which is incorporated herein byreference. The assembly 62 includes a transparent balloon 64 carried atthe end of the body 36. In use, the balloon 64 is inflated with atransparent gas or liquid, thereby providing a viewing window thatshields the fiber optic channels 66 and 68 from blood contact.

The channels includes an incoming optical fiber channel 66, which passesthrough the body 36. The channel 66 is coupled to an exterior source 70of light. The channel 66 conveys lights from the source 70 to illuminatethe tissue region around the balloon 64.

The channels also include an outgoing optical fiber channel 68, whichalso passes through the body 36. The channel 68 is coupled to an eyepiece 72, which can be carried, for example, on the handle 46. Using theeye piece 72, the physician can directly view the illuminated region.

(iii) Other Imaging

The IAE 50 can incorporate other image acquisition techniques. Forexample, the IAE 50 can comprise an apparatus for obtaining an imagethrough optical coherence tomography (OCT). Image acquisition using OCTis described in Huang et al., "Optical Coherence Tomography,"Science,254, Nov. 22, 1991, pp 1178-1181. A type of OCT imaging device, calledan optical coherence domain reflectometer (OCDR) is disclosed in SwansonU.S. Pat. No. 5,321,501, which is incorporated herein by reference. TheOCDR is capable of electronically performing two- and three-dimensionalimage scans over an extended longitudinal or depth range with sharpfocus and high resolution and sensitivity over the range.

As shown in FIG. 25, the IAE 50 comprises the distal end 220 of an opticfiber path 222. The distal end 220 is embedded within an inner sheath224, which is carried within an outer sheath 226. The outer sheath 226extends in the distal body region 40, within the support structure 20.

The inner sheath 224 includes a lens 228, to which the distal fiber pathend 220 is optically coupled. The inner sheath 224 terminates in anangled mirror surface 230, which extends beyond the end of the outersheath 226. The surface 230 reflects optical energy along a path that isgenerally perpendicular to the axis of the distal end 220.

A motor 232 rotates the inner sheath 224 within the outer sheath 226(arrow 237). The lens 228 and the mirror surface 230 rotate with theinner sheath 224, scanning about the axis of rotation. A second motor234 laterally moves the outer sheath 226 (arrows 236) to scan along theaxis of rotation).

A source 238 of optical energy is coupled to the optic fiber path 222through an optical coupler 240. The source 238 generates optical energyof short coherence length, preferably less than 10 micrometers. Thesource 238 may, for example, be a light emitting diode, superluminescent diode, or other white light source of suitable wavelength,or a short-pulse laser.

A reference optical reflector 242 is also coupled by an optic fiber path244 to the optical coupler 240. The optical coupler 240 splits opticalenergy from the source 238 through the optic fiber path 222 to thedistal optic path end 220 and through the optic fiber path 244 to theoptical reflector 242.

The optical energy supplied to the distal optic path end 220 istransmitted by the lens 228 for reflection by the surface 230 towardtissue T. The scanned tissue T (including anatomic structures, otherinternal tissue topographic features, and deposits or lesions on thetissue) reflects the optic energy, as will the surrounding supportstructure 20. The reflected optic energy returns via the optic path 222to the optical coupler 240.

The optical energy supplied to the reference optical reflector 242 isreflected back to the optical coupler 240 by a corner-cuberetro-reflector 246 and an end mirror 250 (as phantom lines 239 depict).The corner-cube retro-reflector 246 is mounted on a mechanism 248, whichreciprocates the corner-cube retro-reflector 246 toward and away fromthe optical path 244 and an end mirror 250 (as arrows 241 depict). Themechanism 248 preferable moves the corner-cube retro-reflector 246 at auniform, relatively high velocity (for example, greater than 1 cm/sec),causing Doppler shift modulation used to perform heterodyne detection.

The length or extent of movement of the corner-cube retro-reflector 246caused by the mechanism 248 is at least slightly greater than half thescanning depth desired. The total length of the optical path 222 betweenthe optical coupler 240 up to the desired scanning depth point is alsosubstantially equal to the total length of the optical path 244 betweenthe optical coupler 240 and the end mirror 250. Movement of thecorner-cube retro-reflector 246 will cause periodic differences in thereflected path lengths 222 and 244.

Reflections received from the optical path 222 (from the lens 228) andthe optical path 244 (from the end mirror 250) are received by theoptical coupler 240. The optical coupler 240 combines the reflectedoptical signals. Due to movement of the corner-cube retro-reflector 246,the combined signals have interference fringes for reflections in whichthe difference in the reflected path lengths is less than the sourcecoherence length. Due to movement of the corner-cube retro-reflector246, the combined signals also have an instantaneous modulatingfrequency.

The combined output is coupled via fiber optic path 252 to a signalprocessor 254. The signal processor 254 converts the optical output ofthe coupler 240 to voltage-varying electrical signals, which aredemodulated and analyzed by a microprocessor to provide an image outputto a display device 256.

Further details of image acquisition and processing using OCDR are notessential to an understanding of the invention, but can be found in theabove-cited Swanson U.S. Pat. No. 5,321,501.

C. Manipulating the Imaging Probe

Regardless of the particular construction of the IAE 50, the supportstructure 20 positioned about the distal region of the probe 34 remainssubstantially in contact against surrounding tissue mass T as the IAE 50operates to acquire the desired image or profile (see FIGS. 5 to 8). Thesupport structure 20 serves to stabilize the IAE 50 and keep tissue Tfrom contacting and possible occluding the IAE 50.

Stabilizing the IAE 50 is particularly helpful when the geometry ofsurrounding body chamber or passage 100 is dynamically changing, such asthe interior of a heart chamber during systole and diastole. The IAE 50is thereby allowed to visualize tissue and anatomic structures T,without the attendant need for constant positioning and repositioning.The structure 20 thus makes possible the generation of accurate imagesof the targeted body region by the IAE 50.

(i) Manual

In a preferred embodiment (see FIG. 5A), the physician can move the IAE50 within the structure 20 forward and rearward (respectively, arrows101 and 103 in FIG. 5A) by pushing or pulling upon the auxiliary handle46. By torquing the handle 46 (arrows 105 in FIG. 5A), the physician mayalso manually rotate the IAE 50 within the structure 20.

The illustrated and preferred embodiment further includes a mechanism 74for deflecting, or steering, the distal region 40 of the body 36, andwith it the IAE 50, transverse of the axis 89 (as depicted in phantomlines 40 in FIG. 5A).

The construction of the steering mechanism 74 can vary. In theillustrated embodiment, the steering mechanism 74 is of the type shownin U.S. Pat. No. 5,336,182, which is incorporated by reference. Thesteering mechanism 74 of this construction includes an actuator 76 inthe auxiliary handle 46. In the illustrated embodiment, the actuator 76takes the form of a cam wheel rotated by means of an external steeringlever 78. The cam wheel 76 holds the proximal ends of right and leftsteering wires 80. The steering wires 80 extend from the cam wheel 76and through the body 36. The steering wires 80 connect to the left andright sides of a resilient bendable wire 82 or spring present within thedistal region 40. Rotation of the cam wheel 76 places tension onsteering wires 80 to deflect the distal region 40 of the body 36, and,with it, the IAE 50 (as shown by arrows 107 in FIG. 5A).

Thus, the physician can manually move the IAE 50 with respect to thestructure 20 in three principal directions. First, the IAE 50 can bemoved along the axis 86 of the structure 20 by pushing and pulling onthe auxiliary handle 46 (arrows 101 and 103). Second, the IAE 50 can bemoved rotationally about the axis 86 of the structure 20 by torquing theauxiliary handle 46 (arrows 105). Third, the IAE 50 can be moved in adirection normal to the axis 86 of the structure 20 by operating thesteering mechanism 74 (arrows 107).

By coordinating push-pull and torquing movement of the handle 46 withoperation of the steering lever 78, the physician can manually move theIAE 50 in virtually any direction and along any path within thestructure 20. The IAE 50 can thereby image tissue locations either incontact with the exterior surface of the structure 20 or laying outsidethe reach of the structure 20 itself.

(ii) Automated (Acquiring Image Slices)

FIG. 9 shows an electromechanical system 102 for manipulating the IAE 50within the structure 20. The system 102 synchronizes the imaging rate ofthe IAE 50 with movement of the IAE 50 within the structure 20. Thesystem allows the physician to use the structure 20 to accuratelyacquire a set of image slices, which can be processed in an automatedfashion for display.

The details of the system 102 can vary. As shown in FIG. 9, the system102 includes a longitudinal position translator 104 mechanically coupledto the probe handle 46. The translator 104 includes a stepper motor 106that incrementally moves an axial screw 111 attached to the handle 46.The motor 106 rotates the screw 111 to move the IAE 50 at a specifiedaxial translation rate within the structure 20, either forward (arrows101) or rearward (arrows 103). As FIG. 9 shows, during axialtranslation, the distal body region 40 carrying the IAE 50 is preferablymaintained in a generally straight configuration, without transversedeflection. By synchronizing the axial translation of the IAE 50 withinthe structure 20 with the imaging rate of the IAE 50, the system 102provides as output axially spaced, data sample slices of the regionsurrounding the IAE 50.

For example, the use of an axial translator 104 of the general typeshown in FIG. 4 in combination with a rotating transducer crystal 52 ofthe type shown in FIG. 6 is described in U.S. Pat. No. 5,485,846, whichis incorporated herein by reference. By rotating the transducer crystal52 in synchrony with the axial translation rate of the translator 104,the system 102 provides axially spaced, 360° data sample slices of theregion perpendicular to the transducer crystal 52. Conventional signalprocessing techniques are used to reconstruct the data slices taken atspecified intervals along the axis into three-dimensional images fordisplay. This technique is well suited for acquiring images inside bloodvessels or other body regions having a known, relatively stablegeometry.

When used to acquire images inside a beating heart chamber, the steppermotor 106 is preferable gated by a gating circuit 190 (see FIG. 9) tothe QRS of an electrocardiogram taken simultaneously with imagegathering, for example, by using a surface electrode 188 shown in FIG.9. The gating circuit 190 is also synchronized with the imaging system54 (as described in greater detail in conjunction with FIG. 6), so thatthe data image slices are recorded in axial increments at eitherend-diastolic or end-systolic points of the heart beat. When imaging anatrium, the data slice recordings are preferably gated to the p-wave.When imaging a ventricle, the imaging is preferably gated to the r-wave.

Alternatively, the circuit 190 is gated to the timing of localintracardiac electrogram activation. In this arrangement (see FIG. 21),the flexible body 36, which carries the transducer 54 within thestructure 20, also carries an electrode 184 to sense electrograms in theregion of the structure 20. The sensed electrograms are conveyed to thecircuit 190 to gate the stepper motor 106, as before described. Whenimaging an atrium, the data slice recordings are gated to the atrialintracardiac electrogram activation. Likewise, when imaging a ventricle,the data slice recordings are gated to the ventricular intracardiacelectrogram activation.

As FIG. 21 shows, the body 36 carrying the transducer 54 and theelectrode 184 is preferably confined for movement within a straight,generally rigid sheath 186. The sheath 186 guides the body 36 along aknown, stable reference axis 183.

The sheath 186 is also preferably constructed of an ultrasonicallytransparent material, like polyethylene. The transducer 54 and electrode184 move in tandem within the confines of the sheath 186 (as shown byarrows 187 and 189 in FIG. 21) in response to the gated action of thestepper motor 106. Because the sheath 186 is ultrasonically transparent,the transducer 54 can remain within the confines of the sheath 186 whileacquiring images. Nonlinearities in image reconstruction caused bydeflection of the transducer outside of the axis 183, as would occurshould the transducer 54 move beyond the sheath 186, are avoided. Theacquired data image slices, position-gated by the electrograms whilemaintained along a known, stable reference axis 183, are generated foraccurate reconstruction into the desired three-dimensional image.

Alternatively, a catheter tracking system as described in Smith et al.U.S. Pat. No. 5,515,853 may be used to track the location andorientation of the IAE 50 during movement. Another system that can beused for this purpose is disclosed in copending U.S. patent applicationSer. No. 08/717,153, filed Sep. 20, 1996 and entitled "Enhanced Accuracyof 3-Dimensional Intraluminal Ultrasound (ILUS) Image Reconstruction,"naming Harm TenHoff as an inventor.

(iii) Localized Guidance

The structure 20 itself can establish a localized position-coordinatematrix about the IAE 50. The matrix makes it possible to ascertain andthereby guide the relative position of the IAE 50 within the structure20 (and thus within the targeted body cavity), to image specific regionswithin the targeted body cavity.

In this embodiment (see FIG. 10), the IAE 50 carries an electrode 31 fortransmitting electrical energy. Likewise, each spline 22 carries anarray of multiple electrodes 30 for transmitting electrical energy.

In the illustrated embodiment (see FIG. 11), the electrodes 30 aresupported about the core body 84 on the flexible, electricallynonconductive sleeve 32, already described. The electrodes 30 areelectrically coupled by wires (not shown), which extend beneath thesleeve 32 through the catheter tube 12 to external connectors 32, whichthe handle 18 carries (see FIG. 1).

In the illustrated embodiment, each electrode 30 comprises a solid ringof conductive material, like platinum, which is pressure fitted aboutthe sleeve 32. Alternatively, the electrodes 30 comprise a conductivematerial, like platinum-iridium or gold, coated upon the sleeve 32 usingconventional coating techniques or an ion beam assisted deposition(IBAD) process. Still alternatively, the electrodes 30 comprise spacedapart lengths of closely wound, spiral coils wrapped about the sleeve32. The coils are made of electrically conducting material, like copperalloy, platinum, or stainless steel. The electrically conductingmaterial of the coils can be further coated with platinum-iridium orgold to improve its conduction properties and biocompatibility. Furtherdetails of the use of coiled electrodes are found in U.S. Pat. No.5,545,193 entitled "Helically Wound Radio-Frequency Emitting Electrodesfor Creating Lesions in Body Tissue," which is incorporated herein byreference.

In yet another alternative embodiment, the electrodes 30 can be formedas part of a ribbon cable circuit assembly, as shown in pending U.S.application Ser. No. 08/206,414, filed Mar. 4, 1994, which isincorporated herein by reference.

In this arrangement (see FIG. 10), a micro-processor controlled guidanceelement 108 is electrically coupled to the electrodes 30 on thestructure 20 and the electrode 31 carried by the IAE 50. The element 108conditions the electrodes 30 on the structure 20 and the IAE electrode31 to generate an electric field (shown in phantom lines 113 in FIG. 10)within the structure 20, while also sensing electrode electricpotentials in the electric field. More particularly, the element 108commands a transmitting electrode, which can be either the IAE electrode31 or at least one of the electrodes 30 in the structure 20, to transmitelectrical energy. The element 108 commands a sensing electrode, whichalso can be either the IAE electrode 31 or at least one of theelectrodes 30 on the structure 20, to sense electrical energy emitted bythe emitting electrode.

The element 108 generates an output by analyzing spatial variations inthe electrical potentials within the field 113, which change based uponthe relative position of the IAE electrode 31 relative to electrode 30on the structure 20. The variations can comprise variations in phase,variations in amplitude, or both. Alternatively, the element 108generates an output by analyzing spatial variations in impedancesbetween the transmitting and sensing electrodes. The output locates theIAE 50 within the space defined by the structure 20, in terms of itsposition relative to the position of the multiple electrodes 30 on thestructure 20.

The element 108 includes an output display device 110 (e.g., a CRT, LEDdisplay, or a printer), which presents the position-identifying outputin a real-time format most useful to the physician for remotely guidingthe IAE 50 within the structure 20.

Further details of establishing a localized coordinate matrix within amultiple electrode structure for the purpose of locating and guiding themovable electrode within the structure are found in copending U.S.patent application Ser. No. 08/320,301, filed Oct. 11, 1994 and entitled"Systems and Methods for Guiding Movable Electrode Elements WithinMultiple Electrode Structures." This application is incorporated hereinby reference.

In a preferred embodiment (see FIG. 26), structure 20 carries anidentification component 270. The identification component 270 carriesan assigned identification code XYZ. The code XYZ identifies the shapeand size of the structure 20 and the distribution of electrodes 30carried by the structure 20, in terms of the number of electrodes andtheir spatial arrangement on the structure 20. The structure-specificinformation contained in the code XYZ aids the element 108 in creating apositioning matrix using the electrodes 30, to help guide the IAE 50within the structure 20.

In the illustrated embodiment (see FIG. 26), the coded component 270 islocated within the handle 46 attached to the proximal end 14 of thecatheter tube 12 that carries the structure 20. However, the component270 could be located elsewhere in relation the structure 20.

The coded component 270 is electrically coupled to an externalinterpreter 278 when the structure 20 is coupled to the element 108 foruse. The interpreter 278 inputs the code XYZ that the coded component270 contains. The interpreter 278 electronically compares the input codeXYZ to, for example, a preestablished master table 280 of codescontained in memory. The master table 280 lists, for each code XYZ, thestructure-specific information required to create the positioning matrixto guide the IAE 50 within the structure 20.

The element 108 preferably includes functional algorithms 288 which setguidance parameters based upon the code XYZ. These guidance parametersare used by the signal processing component 274 of the element inanalyzing the spatial variations of the electric field created withinthe structure 20 to guide the IAE 150. The guidance parameters are alsoused to create the position-identifying output displayed on the device110.

Because knowledge of the physical characteristic of the structure 20 andthe spatial relationship of the electrodes 30 is important in settingaccurate guidance parameters, the algorithms 288 preferably disable theguidance signal processing component 274 in the absence of arecognizable code XYX. Thus, only structures 20 possessing a codedcomponent 270 carrying the appropriate identification code XYZ can beused in association with the element 108 to guide the IAE 50.

The coded component 270 can be variously constructed. It can, forexample, take the form of an integrated circuit 284 (see FIG. 27), whichexpresses in digital form the code XYZ for input in ROM chips, EPROMchips, RAM chips, resistors, capacitors, programmed logic devices(PLD's), or diodes. Examples of catheter identification techniques ofthis type are shown in Jackson et al. U.S. Pat. No. 5,383,874, which isincorporated herein by reference.

Alternatively, the coded component 270 can comprise separate electricalelements 286 (see FIG. 28), each one of which expressing a individualcharacteristic. For example, the electrical elements 286 can compriseresistors (R1 to R4), comprising different resistance values, coupled inparallel. The interpreter 278 measures the resistance value of eachresistor R1 to R4. The resistance value of the first resistor R1expresses in preestablished code, for example, the number of electrodeson the structure. The resistance value of the second resistor R2expresses in preestablished code, for example, the distribution ofelectrodes on the structure. The resistance value of the third resistorR3 expresses in preestablished code, for example, the size of thestructure. The resistance value of the fourth resistor R4 expresses inpreestablished code, for example, the shape of the structure.

Alternatively, the electrodes 30/31 can define passive markers that, inuse, do not transmit or sense electrical energy. The markers aredetected by the physician using, for example, external fluoroscopy,magnetic imaging, or x-ray to establish the location of the structure 20and the IAE 50.

D. Multiple Phased Transducer Arrays

The stability and support that the structure 20 provides the IAE 50 iswell suited for use in association with an IAE 50 having one or morephased array transducer assemblies. The stability and support providedby the structure 20 make it possible to accommodate diverse numbers andlocations of phased array transducers in close proximity to tissue, tofurther enhance the resolution and accuracy of images created by the IAE50.

In one embodiment, as FIG. 22 shows, the structure 20 carries an IAE 50comprising a phased array 192 of ultrasonic transducers of the typeshown, for example, in Shaulov U.S. Pat. 4,671,293, which isincorporated herein by reference. As FIG. 22 shows, the array 192includes two groups 194 and 196 of electrodes. The electrode groups 194and 196 are differently partitioned by channels 206 on opposite faces orplanar sectors 194' and 196' of a piezoelectric material 198. Thechannels 206 cut through the electrode surfaces partially into andthrough the piezoelectric material 198 to prevent mechanical andelectrical coupling of the elements.

The channels 206 on the planar section 194' create spaced transducerelements 202a, 202b, 202c, etc. Likewise, the channels 206 on the planarsection 196' create spaced transducer elements 204a, 204b, 204c, etc.

The electrode groups 194 and 196 are alternatively pulsed by aconventional phase array circuit 200. During one pulse cycle, theelectrode element group 194 is grounded, while the transducer elements204a, 204b, 204c, etc. on the other planar section 196' aresimultaneously pulsed, with the phase relationship of the stimulationamong the transducer elements 204a, 204b, 204c, etc. set to create adesired beam angle, acquiring an image along the one planar sector 196'.During the next pulse cycle, the other electrode element group 196 isgrounded, while the transducer elements 202a, 202b, 202c, etc. on theother planar section 194' are likewise simultaneously pulsed, acquiringanother image along the planar sector 194'. Further details, notessential to the invention, are provided in Haykin, Adaptive FilterTheory, Prentice-Hall, Inc. (1991), pp. 60 to 65.

The signals received by the transducer groups 202a, 202b, 202c, etc. and204a, 204b, 204c, etc., when pulsed, are processed into amplitude,phase, frequency, and time response components. The processed signalsare compared to known configurations with varying transducers activatedto produce and measure the desired waveform. When signals fromcombinations of transducers are processed, a composite image isproduced.

The phased array 192 shown in FIG. 22 permits the real time imaging oftwo different planar sectors, which can be at any angle with respect toeach other.

FIGS. 23 and 24 show other embodiments of an IAE 50 comprising a phasedarray of transducers carried within the structure 20.

In the embodiment shown in FIG. 23, the IAE 50 comprises an array offlexible spline elements 208 having a known geometry. The splineelements 208 are carried within the support structure 20, which itselfcomprises a larger diameter array of flexible spline elements 22, aspreviously discussed in conjunction with FIG. 1. Each flexible splineelement 208 carries a grouping of multiple ultrasonic transducers 210.

Collapsing the outer structure 20 of spline elements 22 by advancing thesheath 44 (previously described and shown in FIGS. 1 and 2) alsocollapses the inner IAE structure of spline elements 208. The mutuallycollapsed geometry presents a low profile allowing joint introduction ofthe structures 22 and 208 into the desired body region.

In the embodiment shown in FIG. 24, the IAE 50 comprises anexpandable-collapsible body 212 carried within the support structure 20.Again, the structure 20 is shown as comprising the array of flexiblespline elements 22. Like the flexible spline elements 208 shown in FIG.23, the exterior surface of the body 212 carries an array of multipleultrasonic transducers 210.

An interior lumen 214 within the body 216 carrying the IAE 50 conducts afluid under pressure into the interior of the body 212 (as shown byarrows 213 in FIG. 24) to inflate it into a known expanded geometry foruse. In the absence of the fluid, the body 212 assumes a collapsedgeometry (not shown). The advanced sheath 44 envelopes the collapsedbody 212, along with the outer structure 20, for introduction into thedesired body region.

In the illustrated embodiment, the ultrasonic transducers 210 are placedupon the spline elements 208 or expandable body 212 (which will becollectively called the "substrate") by depositing desired transducermaterials or composites thereof onto the substrate. Ion beam assisteddeposition, vapor deposition, sputtering, or other methods can be usedfor this purpose.

To create a spaced apart array of transducers 210, a masking material isplaced on the substrate to keep regions free of the deposited material.Removal of the masking material after deposition of the transducermaterials provides the spaced apart array on the substrate.Alternatively, an etching process may be used to selectively removesectors of the transducer material from the substrate to form thedesired spaced apart array. The size of each deposited transducer 210and the density of the overall array of transducers 210 should bebalanced against the flexibility desired for the substrate, asconventional transducer material tends to be inherently stiffer than theunderlying substrate.

Alternatively, transducers 210 can be attached in a preformed state byadhesives or the like to the spline elements 208 or flexible body 212.Again, the size of each attached transducer 210 and the density of theoverall array of transducers 210 should be balanced against theflexibility desired for the substrate.

Signal wires may be coupled to the transducers 210 in various ways afteror during deposition or attachment; for example by soldering, or byadhesive, or by being deposited over. Various other ways to couplesignal wires to solid or deposited surfaces on an expandable-collapsiblebody are discussed in copending patent application Ser. No. 08/629,363,entitled "Enhanced Electrical Connections for Electrode Structures,"filed Apr. 8, 1996, which is incorporated herein by reference.

The signal wires may be bundled together for passage through theassociated catheter tube 12, or housed in ribbon cables for the samepurpose in the manner disclosed in Kordis U.S. Pat. No. 5,499,981, whichis incorporated herein by reference.

It should be appreciated that the multiple ultrasonic transducers 210could be supported on other types of bodies within the structure 20. Forexample, non-collapsible hemispherical or cylindrical bodies, havingfixed predetermined geometries, could occupy the interior of thestructure 20 for the purpose of supporting phased arrays of ultrasonictransducers 210. Alternatively, the signal wires and transducers may bebraided into a desired three-dimensional structure. The braidedstructure may further be laminated to produce an inflatable balloon-likestructure. The dimensions of these alternative transducer support bodiescan vary, subject to the requirement of accommodating introduction anddeployment in an interior body region.

Other examples of phased arrays of multiple transducers are found, forexample, in Griffith et al. U.S. Pat. No. 4,841,977 and Proudian et al.U.S. Pat. No. 4,917,097.

Phased arrays of multiple transducers may be used in association withgating techniques, described above in conjunction with FIG. 9, to lessenthe image acquisition time. In the dynamic environment of the heart,gating may be used to synchronize the phased acquisition of multipleplane images with the QRS or intracardiac electrogram activation,particularly if it is desired to analyze the images over more than oneheart beat.

E. Visualization During Cardiac Mapping Procedures (i) ElectricalActivity Sensing

As just shown (see FIG. 10) and described, the structure 20 can carry anarray of electrodes 30 for the purpose of guiding the IAE 50. These sameelectrodes 30 can also serve to sense electrical impulses in tissue,like myocardial tissue. This sensing function in heart tissue iscommonly called "mapping."

As FIG. 10 shows, when deployed for use inside a heart chamber, thesupport structure 20 holds the electrodes 30 in contact against theendocardium. The electrodes sense the electrical impulses within themyocardium that control heart function. In this arrangement the element108 includes or constitutes an external signal processor made, forexample, by Prucka Engineering, Inc. (Houston, Tex.). The processedsignals are analyzed to locate aberrant conductive pathways and identifyfoci. The foci point to potential ablation sites.

Alternatively, or in combination with mapping, the electrodes 30 on thesupport structure 20 can be used to derive an electrical characteristic,such as impedance, in heart tissue for the purpose of characterizingtissue and locating aberrant conductive pathways. Systems and methodsfor deriving an electrical characteristic of tissue for this purpose aredisclosed, for example, in Panescu et al U.S. Pat. No. 5,494,042, whichis incorporated herein by reference. An electrical characteristic isderived by transmitting electrical energy from one or more electrodesinto tissue and sensing the resulting flow of electrical energy throughthe tissue.

The IAE 50 carried within the multiple electrode structure 20 greatlyassists the physician in mapping or characterizing tissue, whether inthe heart or elsewhere in the body, by locating the electrodes 30 in thedesired orientation with respect to selected anatomic sites. Forexample, when used within the heart, the physician can manipulate theIAE 50 in the manners previously described to visual identify thecoronary sinus, heart valves, superior and inferior vena cava, the fossaovalis, the pulmonary veins, and other key anatomic sites in the heart.Relying upon the visual information obtained by the IAE 50, thephysician can then orient the multiple electrode structure 20 withrespect to one or more of these anatomic sites. Once properly oriented,the physician can further visualize with the IAE 50, to assure that allor a desired number of the electrodes 30 carried by the structure 20 arein intimate contact with tissue required for good signal transmission orgood signal acquisition.

As FIG. 12 shows, the IAE 50 can also be used to help visually steer aseparate mapping electrode 112, carried on its own catheter tube 121,outside or within the support structure 20 into the desired location incontact with heart tissue. If the roving electrode 112 is present withinthe confines of the support structure 20, the structure 20 also servesto stabilize the electrode 112. The guidance processing element 108 aspreviously described (see FIG. 10) can be used in association with thestructure 20 to electronically home the external mapping electrode 112to a desired location within the structure 20.

(ii) Contrast Echocardiography

FIG. 8 shows a system 170 that includes the structure 20 carrying an IAE50 to identify perfusion patterns in myocardial tissue and, thereby,diagnose potential ablation sites within the heart. In this embodiment,the IAE 50 carried within the structure 20 comprises a rotatingultrasonic transducer 52 of the type previously described in conjunctionwith FIG. 6. The system 170 shown in FIG. 8 also preferably includes anelectro-mechanical system 102 for incrementally moving the transducer 52within the structure 20 to obtain axially spaced, data sample slices ofthe region surrounding the transducer 52. The details of this the system102 have been previously described in conjunction with FIG. 9. Theelectro-mechanical system 102 may also be gated to the QRS of anelectrocardiogram or to intracardiac electrogram activation to acquireimages at either end-diastolic or end-systolic points of the heartcycle, in the manner also previously described in conjunction with FIGS.9 or 21.

The system 170 shown in FIG. 8 includes a separate catheter 172. Thecatheter 172 includes an interior lumen 174, which is coupled to asource of an echoluscient contrast media 176. The catheter 172 injectsthe media 176 into the blood stream.

The echoluscient contrast media 176 used may vary. In a preferredembodiment, the media 176 comprises sonicated albumin microbubbles, ortheir equivalent, having a diameter smaller than red blood cells (whichare typically about 8 μm).

When carried within the blood stream, the microbubbles in the media 176are perfused into tissue, just as the blood components that accompanythem. The microbubbles in the media 176, perfused into tissue, stronglyscatter ultrasonic waves. They appear ultrasonically "bright" incontrast to the less ultrasonically "bright" cellular components ofblood also perfused into tissue. The physician is thereby able toaccurately observe the patterns of perfusion of the media 176 intotissue. The more volume of media 176 perfused into tissue, the brighterthe ultrasonic image, and vice versa.

Myocardial tissue that has been infarcted has significantly lowerperfusion characteristics than healthy myocardial tissue. See, forexample, Nath et al., "Effects of Radiofrequency Catheter Ablation onRegional Myocardial Blood Flow," Circulation, 1994; 89: 2667-2672; andVillaneuva et al., "Assessment of Risk Area During Coronary Occlusionand Infarct Size After Reperfusion with Myocardial ContrastEchocardiography Using Left and Right Atrial Injections of Contrast,"Circulation, 1993; 88:596-604).

As FIG. 8 shows, the catheter 172 is preferably maneuveredpercutaneously into a selected coronary vessel. The contrast media 176is injected through the catheter lumen 174 into the vessel, and thusinto the vascular system near the heart.

If the selected vessel is the coronary artery, the media 176 isdistributed throughout the regions of the heart perfused by the coronaryartery, increasing the resolution and contrast in a selected localizedregion. More global distribution of contrast media 176 can be obtainedby selecting an injection site in one of the heart chambers or in thepulmonary artery.

For example, if myocardial tissue in the basil or posterio-lateralaspect of the left ventricle is slated for diagnosis, the catheter 172is preferably maneuvered to inject the media 176 into the circumflexcoronary artery branch of the left main artery. If myocardial tissue inthe anterior aspect of the right or left ventricles is slated fordiagnosis, the catheter 172 is preferably maneuvered to inject the media176 into the left anterior descending (LAD) coronary artery branch ofthe left main artery. If myocardial tissue in the free wall of the rightventricle or the posterior ventricular septum is slated for diagnosis,the catheter 172 is preferably maneuvered to inject the media 176 intothe right coronary artery.

Alternatively, the media 176 can be injected directly into the leftatrium or left ventricle. In this arrangement, the body 36 carrying thetransducer 52 can also include an interior lumen 178 to convey the media176. This approach may be easier and potentially less traumatic thaninjection directly into the coronary artery. However, a portion of themedia 176 will still be dispersed past the coronary arteries and throughthe systemic arterial system, thereby resulting in a poorer resolutionper given volume of media 176 injected. Therefore, a larger volume ofmedia 176 should be injected directly into the left atrium or ventricleto obtain contrast in myocardial tissue comparable to a smaller volumeof media 176 injected directly into a coronary artery, as describedabove.

Furthermore, contrast media 176 may be injected systemically into thefemoral vein. Again, with this approach, significant portions of themedia 176 will be disbursed within the circulatory system, and, inparticular, into the lungs. As just discussed, a larger volume of media176 should be injected systemically into the femoral vein to obtaincontrast in myocardial tissue comparable to a smaller volume of media176 injected directly into a coronary artery.

The system 170 includes a receiver and processor 180 and display device182, as earlier described in conjunction with FIG. 6. In synchrony withthe axial translation system 102, the receiver and processor 180preferably creates a three-dimensional image for display on the device182. Alternatively, an echocardiographic image may be created fordisplay without using the axial translation system 102.

The contrast media 176 highlights the differences in perfusion inmyocardial tissue surrounding the structure 20. Regions of infarctedtissue are visually characterized, as they are not well perfused withblood and appear in negative contrast to the healthy tissue regions thatare well perfused. The same visually characterized, negative contrastregions of infarcted tissue may also form part of the pathways of slowconduction of electrical impulses. These slow conduction pathways may bea substrate for ventricular tachycardia and therefore candidates forcardiac ablation. These candidate regions of slow conduction pathwayswill, in the presence of the contrast media 186, appear on theultrasonic device 182 as zones of negative contrast, being significantlyless ultrasonically "bright" than well perfused tissue regions. Thecandidate regions of slow conduction will typically have infarctedtissue interspersed with well perfused tissue. The candidate regionswill therefore appear ultrasonically "mottled", with patchy regions ofdarker contrast interspersed with lighter contrast. The mottled zoneswill appear contiguous to negative contrast areas. The image resolutionof the device 182 should preferably be fine enough to discern amongmottled zones, light contrast zones, and dark contrast zones.

The support structure 20 maintains the transducer 54 in a stable,substantially unobstructed viewing position near the targeted tissueregion. The transducer 54 thereby generates ultrasonic images of thedifferences in perfusion of the media 176 throughout the imaged hearttissue. The system 170 therefore make possible the accuratecharacterization of tissue for identifying potential ablation sitesusing contrast echocardiography.

In addition to identifying candidate ablation sites, the stable,unobstructed perfusion images that the system 170 provides, also make itpossible to discern the lesion characteristic required to treat thearrhythmia. The perfusion pattern may indicate a localized, containedmottled contrast area, suited for treatment by creating an equallylocalized, small surface area lesion. Alternatively, the perfusionpattern may indicate a larger or deeper mottled contrast area, or amottled contrast area that is elongated or a random complex ofdifferent, intersecting geometries. These instances give rise to theneed for corresponding larger or deeper lesion patterns, or long orintersecting legion patterns, or lesion patterns otherwise havinggeometries tailored to the geometry of the mottled contrast area.

The stable, unobstructed perfusion images that the system 170 providesalso make it possible to characterize tissue substrates associated withpolymorphic ventricular tachycardia. The system 170 makes it possible tocharacterized these regions using echocardiography during normal sinusrhythm. Conventional mapping of electrical events requires induction ofsometimes hemodynamically unstable rhythms to locate and ablatesubstrates associated with polymorphic ventricular tachycardia.

The stable, unobstructed perfusion images that the system 170 providesalso make it possible to discern intermediate contrast zones between"bright" (well perfused tissue) images and negative contrast (not wellperfused, infarcted tissue) images. These intermediate contrast zonesalso delineate the infarcted tissue border. Once identified, tissueablation can be conducted with the objective of ablating tissue withinthe border zone, to eliminate the potential for ventricular tachycardiasubstrates.

The system 170 may characterize tissue morphology based uponechocardiography to locate potential ablation sites in other ways. Forexample, the system 170 may image based upon ultrasonic frequency domainanalyses. For example, the intensity of the second harmonics can be usedto identify tissue morphologies such as scar tissue, ischemic tissue,infarcted tissue, and healthy tissue as a function of tissue elasticity.Frequency domain analyses like second harmonics may be used without theinjection of contrast media 170 to characterize tissue for ablationpurposes.

The system 170 for carrying out contrast echocardiography may alsoincorporate an IAE 50 comprising multiple transducers and using phasedarray techniques to enhance the perfusion images, as previouslydescribed in conjunction with FIGS. 22 to 24.

FIG. 8 shows the system 170 being used in association with intracardiacechocardiography. It should also be appreciated that theechocardiography can be used to characterize tissue morphology, andthereby identify potential ablation sites, using external ultrasoundtransducers located outside the body.

It should also be appreciated that the system 170 can be used as anadjunct to other echography procedures; for example, transesophageal ortransthoracic echography.

The analysis of tissue perfusion patterns to characterize myocardialtissue to locate potential ablation sites can also be accomplished usingexternal imaging techniques other than echography. For example, magneticresonance imaging (MRI) can be used. Using MRI, an isotope, such asgadolinium-chelate, is injected to serve as the contrast material. Asanother example, computerized tomography (CT) scanning can be used.Using CT, iodine radiopaque compounds, such as renografin, can beinjected to serve as the contrast material. As another example, nuclearimaging using thallium as the contrast material can be used. Using anyof these alternative imaging techniques, slow conduction pathways inmyocardial tissue will, in the presence of the appropriate contrastmedia, appear as zones of negative or mottled contrast. As beforediscussed, the image resolution of the alternative technique shouldpreferably be fine enough to discern among mottled zones, light contrastzones, and dark contrast zones. The alternative imaging techniques, likeechography, can also be used to discern intermediate contrast zones,which delineate infarcted tissue borders.

II. Visualization for Therapeutic Purposes

The foregoing description of the structure 20 and associated IAE 50exemplify use in the performance of general diagnostic functions, toaccurately locate and identify abnormalities that may be present in bodycavities or in electrical activities within tissue. The structure 20 andassociated IAE 50 can also aid in providing therapeutic functions, aloneor in combination with these and other diagnostic functions.

The following exemplifies this use in the context of treating cardiacarrhythmias. However, it will be appreciated that there are diverseapplications where the invention can serve therapeutic functions or bothdiagnostic and therapeutic functions.

A. Lesion Formation

Once a potential ablation site has been identified by mapping(typically, in the ventricle), or by reference to an anatomic landmarkwithin the heart (typically, in the atrium), or by deriving anelectrical characteristic, the physician deploys an ablation element tothe site. While various types of ablation energy can be used, in thepreferred implementation, the ablation electrode transmits radiofrequency energy conveyed from an external generator (not shown). Theablation element can takes various forms, depending upon the type oflesion required, which, in turn, depends upon the therapeutic effectdesired.

(i) Smaller Lesions

Typically, lesions that are characterized as "small and shallow" have adepth of about 0.5 cm, a width of about 10 mm, and a lesion volume of upto 0.2 cm³. FIG. 16 exemplifies the geometry for a typical "small"lesion 118. These lesions are desired in the sinus node for sinus nodemodifications, or along the A-V groove for various accessory pathwayablations, or along the slow zone of the tricuspid isthmus for atrialflutter (AFL) or AV node slow pathways ablations. For this purpose, aphysician will typically deploy an electrode having approximately an 8 Fdiameter and a 4 mm length to transmit radio frequency energy to createsmall and shallow lesions in myocardial tissue.

This type of ablation electrode can be used in association with thesupport structure 20, even when the catheter tube bore is occupied bythe imaging probe 34. In this arrangement (see FIG. 12), the physicianseparately deploys the ablation electrode as a "roving" electrode 112outside the support structure 20. The physician then steers the externalelectrode 112 into the confines of the support structure 20 for ablation(such an electrode 112 can also perform an auxiliary mapping function,as already described). Usually, the electrode 112 is preferably operatedin a uni-polar mode during ablation, in which the radio frequencyablation energy transmitted by the electrode 112 is returned through anindifferent patch electrode 114 externally attached to the skin of thepatient.

The support structure 20 serves to stabilize the external "roving"ablation electrode 112 within a confined region of the heart. The IAE 50can be used in this arrangement to help visually navigate the rovingablation electrode 112 into the desired location in contact with hearttissue. The guidance processing element 108 as previously described (seeFIG. 10) can also be used in association with the structure 20 toelectronically home the roving ablation electrode 112 to the desiredablation site contacting the support structure 20.

Alternatively (as FIGS. 5 and 10 show), the electrode 31 that the IAE 50carries can comprise an ablation electrode, in the manner shown in U.S.Pat. No. 5,385,148, which is incorporated herein by reference. Theexterior diameter of the IAE 50 (with electrode 31) is preferably largerthan the interior diameter of the catheter tube bore 38 (see FIG. 5A).Thus, while the IAE 50 (and electrode 31) can be freely moved within thestructure 20 in the manner already described, it cannot be withdrawninto the catheter tube bore.

In this arrangement, the slidable sheath 44 that encloses the structure20 during deployment (see FIG. 2), also encloses the IAE 50 and ablationelement 31 within the collapsed structure 20. Further details of astructure integrating a movable element within a multiple electrodesupport structure can be found in U.S. Pat. No. 5,476,495, which isincorporated herein by reference.

As before explained, the guidance processing element 108 (FIG. 10) canalso create a position-identifying output in a real-time format mostuseful to the physician for guiding the ablation electrode 31 carried bythe IAE 50 within the structure 20 toward a potential site identifiedfor ablation.

In an alternative embodiment, the exterior diameter of the IAE 50 (withelectrode 31) is smaller than the interior diameter of the catheter tubebore 38. The IAE 50 and the entire imaging probe 34 can thereby bewithdrawn through the catheter tube bore 38 from the catheter tube 12.In this arrangement, the catheter tube 12 carrying the multipleelectrode support structure 20 and the imaging probe 34 compriseseparately deployed components. The imaging probe 34 is deployed throughthe catheter tube 12 only when the visualization function is required.When the imaging probe 34 is withdrawn, the catheter tube bore 38 isopen to provide passage for other components; for example, the separatemapping or ablation electrode 112 shown in FIG. 12. In this arrangement,the imaging probe 34 can be switched in situ with the mapping orablation electrode 112, without altering the position of the structure20.

(ii) Larger Lesions

The elimination of ventricular tachycardia (VT) substrates is thought torequire significantly larger and deeper lesions, with a penetrationdepth greater than 1.5 cm, a width of more than 2.0 cm, with a lesionvolume of at least 1 cm³. There also remains the need to create lesionshaving relatively large surface areas with shallow depths. FIG. 17exemplifies the geometry of a typical larger surface area lesion 120,compared to the geometry of the smaller lesion 118 shown in FIG. 16.

FIGS. 13A and 13B show an alternative embodiment of the invention, whichprovides a composite structure 122 carrying an imaging probe 124 and anablation element 126, which is capable of providing larger lesions. Thecomposite structure 122 (like structure 20 shown in FIG. 1) is carriedat the distal end of a flexible catheter tube 12. The proximal end ofthe catheter tube carries an attached handle 18 for manipulating thecomposite structure in the manners previously described.

The composite structure 122 comprises an expandable-collapsible hollowbody 128 made from a porous transparent thermoplastic or elastomericmaterial. The size of the pores 129 in the body 128 are exaggerated forthe purpose of illustration in FIG. 13A. The entire body 128 may beporous, or the body 128 may include a discrete porous region.

The body 128 carries within it an interior electrode 130, which isformed of an electrically conductive material that has both a relativelyhigh electrical conductivity and a relatively high thermal conductivity.Materials possessing these characteristics include gold, platinum,platinum/iridium, among others. Noble metals are preferred. An insulatedsignal wire 132 is coupled to the electrode 130, which electricallycouples the electrode 130 to an external radio frequency generator 134.

An interior lumen 136 within the catheter tube 12 conducts anelectrically conductive liquid 140 under pressure from an externalsource 138 into the hollow interior of the expandable-collapsible body128. As FIG. 13A shows, the electrically conductive liquid 140 inflatesthe body 128 to an enlarged, or expanded, geometry. As will be explainedlater, it is this expanded geometry that makes possible the formation ofthe larger lesions desired. As FIG. 13B shows, in the absence of thefluid 140, the expandable-collapsible body 128 assumes a collapsed, lowprofile. It is this low profile that permits straightforwardintroduction of the structure 122 into the body.

When radio frequency energy is transmitted by the interior electrode130, the electrically conductive liquid 140 within the body 128establishes an electrically conductive path. The pores of the porousbody 128 establish ionic transport of ablation energy from the electrode130, through the electrically conductive liquid 140, to tissue outsidethe body. The paths of ionic transport are designated by arrows 142 inFIG. 13A.

Preferably, the liquid 140 possesses a low resistivity to decrease ohmicloses, and thus ohmic heating effects, within the body 128. Thecomposition of the electrically conductive liquid 140 can vary. In theillustrated and preferred embodiment, the liquid 140 comprises ahypertonic saline solution, having a sodium chloride concentration at ornear saturation, which is about 9% weight by volume. Hypertonic salinesolution has a low resistivity of only about 5 ohm.cm, compared to bloodresistivity of about 150 ohm.cm and myocardial tissue resistivity ofabout 500 ohm-cm.

Alternatively, the composition of the electrically conductive liquid 140can comprise a hypertonic potassium chloride solution. This medium,while promoting the desired ionic transfer, requires closer monitoringof the rate at which ionic transport 142 occurs through the pores, toprevent potassium overload. When hypertonic potassium chloride solutionis used, it is preferred to keep the ionic transport rate below about 10mEq/min. The imaging probe 124 is also located within the body 128. Asbefore described, the probe 124 includes a flexible body 36, whichextends through a central bore 38 and a hemostatic valve (not shown) atthe distal end of the catheter tube 12. The body 36 has a distal region40 that projects beyond the distal end 16 of the catheter tube 12 intothe interior of the support structure 20. The distal body region 40carries an IAE 150, which is sealed from the surrounding liquid 140, forexample, within a housing. Like IAE 50 before described, the IAE 150generates visualizing signals representing an image of objectssurrounding the body 128.

As before explained in conjunction with FIG. 5A, the IAE 150 ispreferably carried for forward and rearward movement by pushing orpulling upon the body 36. The IAE 150 is also preferably movabletransverse of the body axis by the provision of a steering mechanism 76in the distal region 40, as already described.

The IAE 150 can be variously constructed, depending upon thetransparency of the body 128 to imaging energy.

For example, if the body 128 is transparent to optical energy, the IAE150 can comprise a fiber optic channel, as already generally described(see FIG. 7 or FIG. 25). Regenerated cellulose membrane materials,typically used for blood oxygenation, dialysis, or ultrafiltration, canbe made to be optically transparent. Regenerated cellulose iselectrically non-conductive; however, the pores of this material(typically having a diameter smaller than about 0.1 μm) allow effectiveionic transport 142 in response to the applied RF field. At the sametime, the relatively small pores prevent transfer of macromoleculesthrough the body 128, so that pressure driven liquid perfusion throughthe pores 129 is less likely to accompany the ionic transport 142,unless relatively high pressure conditions develop within the body 128.

Regenerated cellulose is also transparent to ultrasonic energy. The IAE50 can thus alternatively comprise an ultrasonic transducer crystal, asalso already described (see FIG. 6).

Other porous materials, which are either optically transparent orotherwise transparent to the selected imaging energy, can be used forthe body 128. Candidate materials having pore sizes larger thanregenerated cellulous material, such as nylon, polycarbonate,polyvinylidene fluoride (PTFE), polyethersulfone, modified acryliccopolymers, and cellulose acetate, are typically used for bloodmicrofiltration and oxygenation. Porous or microporous materials mayalso be fabricated by weaving a material (such as nylon, polyester,polyethylene, polypropylene, fluorocarbon, fine diameter stainlesssteel, or other fiber) into a mesh having the desired pore size andporosity. These materials permit effective passage of ions in responseto the applied RF field. However, as many of these materials possesslarger pore diameters, pressure driven liquid perfusion, and theattendant transport of macromolecules through the pores, are also morelikely to occur at normal inflation pressures for the body 128.Considerations of overall porosity, perfusion rates, and lodgment ofblood cells within the pores of the body 128 must be taken more intoaccount as pore size increase.

Low or essentially no liquid perfusion through the porous body 128 ispreferred. Limited or essentially no liquid perfusion through the porousbody 128 is beneficial for several reasons. First, it limits salt orwater overloading, caused by transport of the hypertonic solution intothe blood pool. This is especially true, should the hypertonic solutioninclude potassium chloride, as observed above. Furthermore, limited oressentially no liquid perfusion through the porous body 128 allows ionictransport 142 to occur without disruption. When undisturbed by attendantliquid perfusion, ionic transport 142 creates a continuous virtualelectrode at the body 128-tissue interface. The virtual electrodeefficiently transfers RF energy without need for an electricallyconductive metal surface.

As shown in FIG. 13A, the porous body 128 serves a dual purpose. Likethe structure 20, the porous body 128 keeps open the interior chamber orpassages within the patient's body targeted for imaging, while at thesame time keeping tissue T away from potential occluding contact withthe IAE 150. The body 128 also helps to stabilize the position of theIAE 50. In these ways, the body 128, like the support structure 20,provides a substantially stationary platform for visualizing tissue andanatomic structures for diagnostic purposes, making possible thecreation of an accurate image of the targeted body cavity.

Furthermore, through the ionic transfer 142 of the RF field generatedwithin the body 128, the porous body 128 also serves the therapeuticfunction as a tissue ablation element. The use of a porous body 128,expanded after introduction to an enlarged diameter (see FIG. 13A),makes possible the creation of larger lesions in a controlled fashion toablate epicardial, endocardial, or intramural VT substrates. By alsocontrolling the porosity, and thus the electrical resistivity of thebody 128, the physician can significantly influence the depth of thelesion. The use of a low-resistivity body 128 results in deeper lesions,and vice versa.

Further details of the use of porous bodies to deliver ablation energythrough ionic transport are found in copending patent application Ser.No. 08/631,356, filed Apr. 12, 1996 and entitled "Tissue Heating andAblation Systems and Methods Using Electrode Structures With DistallyOriented Porous Regions," which is incorporated herein by reference.

In an alternative embodiment, the porous body 128 and IAE 150 canthemselves occupy the interior of a multiple spline support structure146, as shown in FIG. 14. In this arrangement, the exterior multiplespline structure 146 provides added stabilization and protection for theporous body and IAE 150. As shown in FIG. 14, the multiple splinesupport structure 146 may also carry an array of electrodes 148. Theseelectrodes 148 can be used for mapping or characterizing tissue or forguidance of the interior porous ablation body and IAE 150, in themanners previously described.

(iii) Long Lesions

Atrial geometry, atrial anisotropy, and histopathologic changes in theleft or right atria can, alone or together, form anatomic obstacles. Theobstacles can disrupt the normally uniform propagation of electricalimpulses in the atria, resulting in abnormal, irregular heart rhythm,called atrial fibrillation.

U.S. patent application Ser. No. 08/566,291, filed Dec. 1, 1995, andentitled "Systems and Methods for Creating Complex Lesion Patterns inBody Tissue" discloses catheter-based systems and methods that createcomplex long lesion patterns in myocardial tissue. In purpose andeffect, the systems and methods emulate the open heart maze procedure,but do not require costly and expensive open heart surgery. Thesesystems and methods can be used to perform other curative procedures inthe heart as well.

The multiple spline support structure 152 shown in FIG. 15 is wellsuited for therapeutic use in the atrial regions of the heart. In FIG.15, a transeptal deployment is shown, from the right atrium (RA),through the septum (S), into the left atrium (LA), where the supportstructure 152 is located for use.

The longitudinal splines 154 carry an array of electrodes 156. Theelectrodes 156 serve as transmitters of ablation energy. An IAE 50, aspreviously described, is movably carried within the interior of thestructure 152.

The electrodes 156 are preferably operated in a uni-polar mode, in whichthe radio frequency ablation energy transmitted by the electrodes 156 isreturned through an indifferent patch electrode 158 externally attachedto the skin of the patient. Alternatively, the electrodes 156 can beoperated in a bi-polar mode, in which ablation energy emitted by one ormore electrodes 156 is returned an adjacent electrode 156 on the spline154.

The size and spacing of the electrodes 156 shown in FIG. 15 arepurposely set for creating continuous, long lesion patterns in tissue.FIG. 18 shows a representative long, continuous lesion pattern 160,which is suited to treat atrial fibrillation. Continuous, long lesionpatterns 160 are formed due to additive heating effects when RF ablationenergy is applied in a uni-polar mode simultaneously to the adjacentelectrodes 156, provided the size and spacing requirements are observed.The additive heating effects cause the lesion pattern 160 to spanadjacent, spaced apart electrodes 156, creating the desired elongatedgeometry, shown in FIG. 18. The additive heating effects will also occurwhen the electrodes 156 are operated simultaneously in a bipolar modebetween electrodes 156, again provided the size and spacing requirementsare observed.

The additive heating effects between spaced apart electrodes 156intensify the desired therapeutic heating of tissue contacted by theelectrodes 156. The additive effects heat the tissue at and between theadjacent electrodes 156 to higher temperatures than the electrodes 156would otherwise heat the tissue, if conditioned to individually transitenergy to the tissue, or if spaced apart enough to prevent additiveheating effects.

When the spacing between the electrodes 156 is equal to or less thanabout 3 times the smallest of the diameters of the electrodes 156, thesimultaneous emission of energy by the electrodes 156, either bipolarbetween the segments or unipolar to the indifferent patch electrode,creates the elongated continuous lesion pattern 160 shown in FIG. 18 dueto the additive heating effects. Conversely, when the spacing betweenthe electrodes 156 is greater than about 5 times the smallest of thediameters of the electrodes 156, the simultaneous emission of energy bythe electrodes 156, either bipolar between segments or unipolar to theindifferent patch electrode, does not generate additive heating effects.Instead, the simultaneous emission of energy by the electrodes 156creates an elongated segmented, or interrupted, lesion pattern 162 inthe contacted tissue area, as shown in FIG. 20.

Alternatively, when the spacing between the electrodes 156 along thecontacted tissue area is equal to or less than about 2 times the longestof the lengths of the electrodes 156, the simultaneous application ofenergy by the electrodes 156, either bipolar between electrodes 156 orunipolar to the indifferent patch electrode, also creates an elongatedcontinuous lesion pattern 160 (FIG. 18) due to additive heating effects.Conversely, when the spacing between the electrodes 156 along thecontacted tissue area is greater than about 3 times the longest of thelengths of the electrodes 156, the simultaneous application of energy,either bipolar between electrodes 156 or unipolar to the indifferentpatch electrode, creates an elongated segmented, or interrupted, lesionpattern 162 (FIG. 20).

In an alternative embodiment (see FIG. 15), the assembly includesperiodic bridge splines 164. The bridge splines 164 are soldered orotherwise fastened to the adjacent longitudinal splines 154. The bridgesplines 164 carry electrodes 166, or are otherwise made to transmitablation energy by exposure of electrically conductive material. Upontransmission of ablation energy, the bridge splines 166 create longtransverse lesion patterns 168 (see FIG. 19) that span across the longlongitudinal lesion patterns 160 created by the adjacent splines 154.The transverse lesions 168 link the longitudinal lesions 160 to createcomplex lesion patterns that emulate the patterns formed by incisionsduring the surgical maze procedure.

Further details of the creation of complex long lesion patterns in thetreatment of atrial fibrillation are found in copending U.S. applicationSer. No. 08/566,291, filed Dec. 1, 1995, and entitled "Systems andMethods for Creating Complex Lesion Patterns in Body Tissue," which isincorporated herein by reference.

B. Lesion Visualization

The IAE 50/150 associated with the structures shown permits thephysician to visually inspect the lesion pattern during or afterablation to confirm that the desired pattern and depth have beencreated. By manipulating the IAE 50/150 in the manner described aboveduring or after ablation, the physician can view the lesions fromdifferent directions, to assure that the lesion geometry and depthconforms to expectations. The IAE 50/150 can also inspect a long lesionpattern (like patterns 160 or 168 in FIG. 19) during or after ablationfor gaps or interruptions, which could, if present, provide unwantedpathways for aberrant electrical pulses. Contrast echocardiography,employing contrast media (as earlier described in conjunction with FIG.8), may also be used to identify gaps in long lesions during or aftertheir formation. Since perfusion through thermally destroyed tissue issignificantly less than in other tissue, gaps in long lesion patterns(i.e., tissue that has not been thermally destroyed) will, in thepresence of contrast media, appear ultrasonically "brighter" than tissuein the lesion area. Ablation of these gaps, once identified by the IAE50/150, completes the long lesion pattern to assure that the intendedtherapeutic result is achieved.

The IAE 50/150 can also help the physician measure the width, length,and depth of the lesion pattern. Using the IAE 50/150, the physician candirectly measure these physical lesion characteristics, instead of or asan adjunct to predicting such characteristics from measurements ofapplied power, impedance, tissue temperature, and ablation time.

The IAE 50/150 can further help the physician characterize tissuemorphology. Using the IAE 50/150, the physician can visualize borderregions between healthy and infarcted tissue, alone or in combinationwith electrical impulse sensing with the electrodes 156.

Various features of the invention are set forth in the following claims.

We claim:
 1. A system for imaging an interior body region comprisingaprobe including an axis and an imaging structure having a peripheryadapted to selectively assume an expanded geometry and a collapsedgeometry, and an array of spaced apart ultrasound transducers attachedto the periphery of the imaging structure, wherein members of the arraymove radially outward and inward relative to the axis as the peripheryassumes the expanded geometry and the collapsed geometry respectively.2. A system according to claim 1wherein the imaging structure comprisesat least two spaced apart support members.
 3. A system according toclaim 2wherein the support members are made from metal material.
 4. Asystem according to claim 3wherein the metal material includes nickeltitanium.
 5. A system according to claim 3wherein the metal materialincludes stainless steel.
 6. An assembly according to claim 2wherein thesupport members are made from plastic material.
 7. A system according toclaim 2wherein the support members comprise elongated spline elementsassembled in a circumferentially spaced relationship.
 8. A systemaccording to claim 1wherein the imaging structure includes supportmembers and is adapted to assume the collapsed geometry in response toexternal force, the imaging structure being urged by the support memberstoward the expanded geometry in the absence of the force.
 9. A systemaccording to claim 8and further including a sheath slidable relative tothe imaging structure in a first direction to apply external force tourge the support elements into the collapsed geometry and in a seconddirection to release the external force, thereby allowing the supportstructure to assume an expanded geometry.
 10. A system according toclaim 1wherein the imaging structure comprises a three-dimensionalstructure.
 11. A system according to claim 10wherein thethree-dimensional structure comprises an expandable body.
 12. A systemaccording to claim 11wherein the expandable body expands to an expandedgeometry in response to fluid pressure.
 13. A system according to claim11wherein the expandable body collapses in the absence of fluidpressure.
 14. A system according to claim 1wherein the array comprises aphased array ultrasound transducer assembly.
 15. A system according toclaim 1wherein the array comprises coatings each comprising either anultrasound transducer material or an ultrasound transducer materialcomposite deposited in a spaced apart relationship on the periphery ofthe imaging structure.
 16. A system according to claim 15wherein thecoatings are deposited by a technique including either ion beam assisteddeposition, or vapor deposition, or sputtering.
 17. A system accordingto claim 1wherein the array comprises preformed elements each comprisingeither an ultrasound transducer material or an ultrasound transducermaterial composite secured in a spaced apart relationship on theperiphery of the imaging structure.
 18. A system according to claim 1andfurther including a support structure extending beyond the periphery ofthe imaging structure.
 19. A system according to claim 18and furtherincluding at least one electrode carried by the support structure.
 20. Asystem according to claim 18and further including a steering elementcoupled to the imaging structure to move the structure relative to thesupport structure.
 21. A system according to claim 20wherein the supportstructure has an axis, and wherein the steering element moves theimaging structure along the axis.
 22. A system according to claim20wherein the support structure has an axis, and wherein the steeringelement moves the imaging structure transverse to the axis.
 23. A systemaccording to claim 20wherein the support structure has an axis, andwherein the steering element rotates the imaging structure about theaxis.
 24. A system according to claim 20wherein the steering elementincludes an actuator to move the imaging structure in response tocontrol commands.
 25. A system according to claim 20and furtherincluding a steering element coupled to the imaging element to move theimaging structure without moving the support structure.
 26. A method forvisualizing body tissue comprising the steps ofproviding a probe with animaging structure having a periphery adapted to selectively assume anexpanded geometry and a collapsed geometry, and an array of spaced apartultrasound transducers attached to the periphery of the imagingstructure, guiding the probe into an interior body region while causingthe imaging structure to assume the collapsed geometry, causing theimaging structure to assume the expanded geometry upon arrival in theinterior body region, and operating the imaging structure, while in theexpanded geometry, to visualize tissue in the interior body region. 27.A method according to claim 26and further including the step ofgenerating an image of tissue visualized by the imaging structure.
 28. Amethod according to claim 27and further including the step of using theimage to orient the imaging structure.
 29. A method according to claim27and further including the step of using the image to view a lesion.30. A method according to claim 27and further including the step ofusing the image to assess contact between the imaging structure andsurrounding tissue.
 31. A method according to claim 27and furtherincluding the step of using the image to identify thrombus.
 32. A methodaccording to claim 27and further including the step of using the imageto characterize tissue morphology.
 33. A method according to claim26wherein the introducing step includes introducing the imagingstructure into a heart chamber.
 34. A method according to claim 26 andfurther including the step of moving the imaging structure.
 35. A methodaccording to claim 26 and further including the step of moving theimaging element within a support structure that extends beyond theperiphery of the imaging structure.
 36. A method according to claim26and further including the step of moving the imaging structure withina support structure that extends beyond the periphery of the imagingstructure, the imaging structure being moved without moving the supportstructure.
 37. A method according to claim 36wherein the operating stepacquires image slices during the moving step.
 38. A system for imagingan interior body region, comprisinga probe having an imaging structureadapted to selectively assume an expanded geometry and a collapsedgeometry, and an array of ultrasound transducers on the imagingstructure, wherein members of the array move away from one another asthe imaging structure assumes the expanded geometry.
 39. The system ofclaim 38, wherein the imaging structure comprises an expandable body.40. The system of claim 39, wherein the expandable body includes aplurality of spline elements arranged to have a predetermined geometryin the expanded condition.
 41. The system of claim 40, wherein the arrayof ultrasound transducers comprises an ultrasound transducer on each ofthe spline elements.
 42. The system of claim 39, wherein the expandablebody assumes the expanded geometry in response to internal fluidpressure.
 43. The system of claim 38, wherein the array of ultrasoundtransducers comprises a phased array ultrasound transducer assembly. 44.The system of claim 38, wherein the array of ultrasound transducersincludes transducer material deposited on the imaging structure by ionbeam assisted deposition.
 45. The system of claim 38, further comprisinga support structure surrounding the imaging structure.
 46. A system forimaging an interior body region, comprisinga probe including a distalportion, an imaging structure having a predetermined geometry on thedistal portion, a plurality of arrays of ultrasound transducers attachedto the imaging structure in a predetermined arrangement for acquiringimages along a plurality of sectors, and a support structure on theprobe and substantially surrounding the imaging structure, the supportstructure being adapted to assume an expanded geometry and a collapsedgeometry.
 47. The system of claim 46, wherein the probe includes alongitudinal axis, and wherein the support structure expands radiallywith respect to the longitudinal axis as it assumes the expandedgeometry.
 48. The system of claim 46, wherein the imaging structure isan expandable body adapted to assume an expanded geometry and acollapsed geometry.
 49. The system of claim 48, wherein the plurality ofarrays comprises a plurality of phased arrays of ultrasound transducersdisposed on the imaging structure and adapted to move away from oneanother as the imaging structure assumes the expanded geometry.
 50. Thesystem of claim 46, wherein the imaging structure has a fixedpredetermined geometry for supporting the plurality of arrays in thepredetermined arrangement.
 51. The system of claim 50, wherein theimaging structure comprises a hemispherical body or a cylindrical body.